The present invention relates to a super water-repellent organic/inorganic composite membrane, and more particularly to a new-concept super water-repellent organic/inorganic composite membrane having excellent permeability by forming skin layer chemically immobilized with functional polymer on the surface of a porous inorganic support with fractal surface structure and pore size of nanometers to micrometers, using xe2x80x98grafting-fromxe2x80x99 polymerization.
xe2x80x98Membrane separationxe2x80x99 means separating pure molecules from a mixture using physical and chemical properties of membrane. A membrane is a third phase that separates two homogenous phases, whose physical and chemical properties determine the rate of exchanging material and energy through it. FIG. 1 illustrates a schematic diagram of membrane separation. In membrane separation process, all resistance to transfer is focused at skin layer of membrane, and the resistance varies with characteristics of material. Therefore, the rate of transfer through membrane is different from material to material, and it enables separation of materials. The most important factors that affect separation of mixtures through the membrane are pore size of the membrane and chemical properties of the membrane surface. Namely, the pore size and the skin layer with suitable surface characteristics of the membrane should be determined depending on the physical and chemical property of the materials to be separated in the membrane process.
A membrane is classified as polymer membrane and inorganic membrane. The polymer membrane has good separation efficiency because it can endow various properties on the membrane surface. However, it has limitation in operation since polymer material has poor thermal and mechanical stability. On the other hand, the inorganic membrane has advantages in regulating pore size and in high temperature and pressure operation compared to the polymer membrane. However, it is difficult to improve separation efficiency by varying surface functionalities.
In order to solve these problems, organic/inorganic composite membranes with functional polymer film on inorganic support surface have been proposed and actively researched. The organic/inorganic composite membrane can preserve severe operation conditions (the merit of the inorganic membrane), and can have various functionality surfaces (the merit of the polymer membrane). Therefore, it is in the spotlight of researches.
One of the conventional methods of preparing organic/inorganic composite membrane is forming functional surface film on inorganic surface by adsorbing functional polymer solution on inorganic support (This method is called solvent dipping method). With this method, the organic/inorganic composite membrane can be obtained very easily. However, because the polymer surface film of prepared organic/inorganic composite membrane is bonded to the inorganic surface by dispersion force (van der Waals force) only, the durability is poor, and the skin layer can be easily lost resulting the limitation in operation with various environments. The problem of the membrane prepared by the solvent dipping method can be solved by the well known self-assembly method. That is, organic/inorganic composite membrane with chemically bonded functional polymer film can be prepared by grafting-to polymerization, which reacts polymer with reactive functional group on inorganic surface. However, in forming the polymer surface film by grafting-to polymerization, polymer brushes formed by the preceding reaction hinder access of additional reactive polymer to the inorganic surface due to steric hindrance. Accordingly, the more functional polymer film is immobilized on the solid surface, the larger the surface concentration gradient is built-up, and a film with limited thickness (xcx9c20 nm) is formed. Therefore, this method is limited in control of thickness of the surface functional film.
Solid surface with super water-repellent property is widely used in everyday lives and industry. Traditionally, the super water-repellent surface has been prepared by forming fluorinated film on solid surface through physicochemical adsorption methods. However, because fluorinated materials have very low surface free energy, it was very difficult to physicochemically prepare the fluorinated film on solid surface. Also, in order to obtain surface with very superior super water-repellency, geometric structure modification of the solid surface is required, as well as chemical surface modification.
The inventors have developed a functional fluorinated polymer film chemically bonded to inorganic support surface via in-situ surface polymerization using porous inorganic support surface with fractal structure, and self-assembled monolayer of initiator and fluorinated monomer, in order to prepare organic/inorganic composite membrane with easily controllable pore size and surface functionalities which preserve super water-repellency.
Accordingly, an object of this invention is to provide a membrane with superior separation efficiency and operation condition compared to the conventional organic/inorganic composite membrane, with easily controllable pore size and surface functionality and very durable superior water-repellency.